Overview

UV Camera is an iPhone app designed to use the dual-rear cameras of an iPhone XS (or better), in combination with a custom UV filter inserted into the optical path of one camera, to enhance and highlight UV signal within a visual image.

References

• Swift 4 & iOS 11: Custom Camera View (Ep3 of Build a Custom Camera)

Should an Android version float up the priority stack, have a look at this:

• https://medium.com/androiddevelopers/using-multiple-camera-streams-simultaneously-bf9488a29482

Concept of Operations

If we’re specifically looking to find UV absorbance, and as an approximation we’re using shadows which are particularly or uniquely dark in the (380, 410nm) to represent that, then we should be able to bring those out using something like this:

WHERE:

• Suv = Shadows exclusively in the range (380, 410nm) (not appearing in Svis)
• Svis = Shadows anywhere in VIS (410, 740nm)
• Sf = Shadows in filtered camera (380, 410nm)
• Sgr = Shadows in green, red region (500, 740nm)
• Sb = Shadows in blue region (380, 500nm)
• Sb’ = Shadows in blue region, above filter (410, 500nm)

PROCEDURE:

• generate Sf: copy filtered orig; drop green, red channels; grayscale; invert; increase contrast (will show white for shadows in (380, 410); black for light in (380, 410))
• generate Sgr: copy unfiltered orig; drop blue channel; grayscale; invert; increase contrast (white for shadows in (500, 740); black for light in (500, 740))
• generate Sb: copy unfiltered orig; drop green, red channels; grayscale; invert; increase contrast (white for shadows in (380, 500); black for light in (380, 500))
• compute Sb’: Sf - Sb (white for shadows in (410, 500); black for light in (410, 500))
• compute Svis = Sgr + Sb’ (white for shadows in (410, 740); black for light in (410, 740))
• compute Suv = Sf - Svis (white for shadows exclusively in (380, 410))

So then if we tint Suv and blend it atop the original unfiltered image, we should be highlighting regions which are especially low in UV.

Version History

• 2.x (UV Absorbance)

  • 2019-11-11 2.0.13
    • fixed persisting Picker values in State
    • fixed Gamma value/flag mixup
  • 2019-11-11 2.0.12
    • expose Gamma Preset enums as Picker
  • 2019-11-11 2.0.11
    • fixed Settings switches
  • 2019-11-08 2.0.10
    • updated docs
  • 2019-11-07 2.0.9
    • added Settings screen (boolean switch position messed up, not sure why)
    • save/load fully raw images to support re-registration
  • 2019-10-29 2.0.8
    • updated docs
    • added Makefile
  • 2019-10-28 2.0.7
    • added cropVerticalShift
    • added blurBox
    • added posterize
    • fixed adjustWhitePoint? (MAYBE no longer need TintFilter?)
  • 2019-10-25 2.0.6
    • simplified intra-thread variable passing
    • added adjustGamma
    • added adjustWhitePoint
    • putzed around with JPEG flattening, tint3 etc
    • added 3rd-order TintFilter (yay)
  • 2019-10-24 2.0.5
    • added applyGammaPreset
    • processing tweaks
  • 2019-10-23 2.0.4
    • added adjustExposure
    • fixed DropBlueFilter
  • 2019-10-16 2.0.3
    • added "load" button to support offline / nighttime testing
  • 2019-10-16 2.0.2
    • chunked processing into tasks to reduce per-thread memory footprint
  • 2019-10-15 2.0.1
    • fighting memory issues (too many debug saves)
    • kinda sorta seems to work?
  • 2019-10-15 2.0.0
    • redesigned image processing pipeline for UV absorbance
    • added UIImage.copy, .dropBlue, .caption
    • runs, not spectrally evaluated

• 1.x (UV Reflectance)

  • 2019-08-23
    • migrated to GitHub
    • docs
  • 2019-08-22 1.3.0
    • added normalize3()
    • added BlueFilter
    • successful testing with SPF-100 samples
  • 2019-08-22 1.2.4
    • moved default preview session from NFOV to WFOV
    • added adjustContrast()
    • migrating to non-subtractive (filtered) UV acquisition
  • 2019-08-21 1.2.3
    • moved UV filter from WFOV to NFOV
    • added UIImage.invert()
  • 2019-07-22 1.2.2
    • added Launch Screen, online help
    • submitted for TestFlight (approved)
  • 2019-07-19 1.1.3
    • resolved most constraint warnings
    • fixed screens for 6.5", 5.5"
    • better handling of non-dual-camera iPhones
    • first App Store submission (rejected)
  • 2019-07-03 0.0.5
    • 3.5x speedup (removed manual pixel math)
  • 2019-07-02 0.0.4
    • basic image-processing in place
  • 2019-06-11 0.0.3
    • convert to mono
    • crop f/1.8 image to 50%
    • subtract images
  • 2019-03-19 0.0.2
    • able to screenshot previews from both cameras
  • 2019-03-19 0.0.1
    • stubbing views